This invention relates to a process for the preparation of trifluoromethylbenzoyl chlorides and trifluoromethylbenzoyl bromides. The products are useful intermediates for the production of various dyestuffs and agricultural chemical products.
Various methods are known for the preparation of trifluoromethylbenzoyl halides. It is known, for example, to prepare trifluoromethylbenzoyl chloride by reaction of trifluoromethylbenzoic acid with thionyl chloride. The starting material for such reaction, trifluoromethylbenzoic acid may be prepared by several methods, each of which is a multi-stepped process involving relatively expensive starting materials and/or intermediates. Thus, for example, it is known to prepare trifluoromethylbenzoic acid by cyanation of bromo-benzotrifluoride and hydrolysis of the resulting cyanobenzotrifluoride. In another known method, bromo-benzotrifluoride is reacted with magnesium and the resultant Grignard reagent is reacted with carbon dioxide to form trifluoromethylbenzoic acid.
In still another method xylene may be oxidized to toluic acid, the acid group esterified, and the methyl group chlorinated and then fluorinated to yield trifluoromethylbenzoic acid.
Although the processes of the prior art are useful for the preparation of trifluoromethylbenzoyl chloride, it will be appreciated that improvements in the efficiency, economy of preparation and yield of the desired product are nevertheless desirable.
In co-pending application Ser. No. 140,894, filed Apr. 16, 1980, now U.S. Pat. No. 4,500,471, an improved process for the preparation of trifluoromethylbenzoyl chlorides and bromides is disclosed. The process disclosed therein comprises the preparation of trifluoromethylbenzoyl chlorides or bromides by reaction of trichloromethylbenzoyl chlorides or tribromomethylbenzoyl bromides with hydrogen fluoride in the presence of a halogen transfer catalyst. In addition to the desired trifluoromethylbenzoyl chloride or bromide, the reaction product may contain varying amounts of over-fluorinated product, in particular, trifluoromethylbenzoyl fluoride, and various mixed fluoro-bromo or fluorochloro products such as chlorodifluoromethylbenzoyl chloride and the like. The production of such over- or partially fluorinated by-products, even in minor amounts, is economically unattractive and may present additional problems with respect to the proper disposal thereof. It will be appreciated that a simple, economical method for the conversion of such products to the desired trifluoromethylbenzoyl chlorie or bromide product would be particularly useful to avoid the aforementioned economic and disposal problems.
Accordingly, it is an object of the present invention to provide a simple, direct method for the conversion of trihalomethylbenzoyl halide mixtures to trifluoromethylbenzoyl chlorides or bromides. It is a further object to provide a halogen exchange process for the conversion of trifluoromethylbenzoyl fluorides to trifluoromethylbenzoyl chlorides or bromides.